As set forth in U.S. Pat. No. 6,054,057, which is herein incorporated by reference, the process of wet oxidization involves the addition of an oxidizing agent, typically air or oxygen, to an aqueous stream including feed materials at elevated temperatures and pressures. The resultant “combustion” of organic or inorganic oxidizable feed materials occurs directly within the aqueous phase.
For supercritical water oxidization (“SCWO”), oxidization occurs essentially entirely at conditions which are supercritical in both temperature (>374° C.) and pressure (>about 3,200 psi or 220 bar). Importantly, SCWO has been shown to give rapid and complete oxidization of virtually any organic compound in a matter of seconds at five hundred degrees Celsius to six hundred fifty degrees Celsius (500° C.-650° C.) and 250 bar. During this oxidization, carbon and hydrogen in the oxidized material form the conventional combustion products carbon dioxide (“CO2”) and water. When chlorinated hydrocarbons are involved, they give rise to hydrochloric acid (“HCl”), which will react with available cations to form chloride salts. Due to the adverse effects of HCl, alkali may be intentionally added to the reactor to avoid high, corrosive concentrations of hydrochloric acid in the reactor and especially in the cooldown equipment following the reactor. When sulfur oxidization is involved, the final product in SCWO is a sulfate anion. This is in contrast to normal combustion, which forms gaseous sulfur dioxide (“SO2”). As in the case of chloride, alkali may be intentionally added to avoid high concentrations of sulfuric acid. Similarly, the product of phosphorus oxidization is phosphate anion.
At typical SCWO reactor conditions, densities are in the range of 0.1 g/cc, so water molecules are considerably farther apart than they are in ambient liquid water. Hydrogen bonding, a short-range phenomenon, is almost entirely disrupted, and the water molecules lose the ordering responsible for many of liquid water's characteristic properties. In particular, solubility behavior is closer to that of high pressure steam than to liquid water. Smaller polar and nonpolar organic compounds, with relatively high volatility, will exist as vapors at typical SCWO conditions, and hence will be completely miscible with supercritical water. Gases such as N2, O2, and CO2 show similar complete miscibility. Larger organic compounds and polymers will hydrolyze to smaller molecules at typical SCWO conditions, thus resulting in solubilization via chemical reaction. The loss of bulk polarity by the water phase has striking effects on normally water-soluble salts, as well. In particular, because they are no longer readily solvated by water molecules, salts frequently precipitate out as solids that can deposit on process surfaces and cause fouling of heat transfer surfaces or blockage of the process flow.
This precipitation of solids presents a significant problem in industrial uses of SCWO applications. Specifically, one of the key issues that must be addressed in SCWO applications is the energy cost of compressing air for use in the feed material. In order to reduce energy costs, efforts have been made to recover energy from the reactor stream. However, the large quantities of salts and particulates in the reactor stream interfere with the energy recovery devices. Various systems have been proposed to overcome such interference. For instance, some systems have utilized a filter or cyclone device downstream of the reactor to separate the salts and particulates from the stream before energy recovery. However, the salts and particulates often plug the flow of the stream at the reactor. Therefore, the flow must first be quenched to a low enough temperature to form an aqueous phase. Quenching the reactor stream lowers its temperature and reduces the net energy that can be recovered therefrom.
In order to avoid the reduction of recoverable energy, a reversing flow reactor was developed. In such a reactor the flow enters and exits at the top, while a brine pool is maintained at the reactor bottom. While this design addresses the energy recovery issue, it limits the reaction zone to 3-4 L/D before the fluid reverses. Further, it limits the conditions in the reaction zone to a back-mixed zone. As a result, achieving high destruction efficiency in such a reactor requires a large diameter vessel with a high capital cost.
In light of the above, it is an object of the present invention to provide a system and method that provides for separation of the fluid effluent from the salts and particulates resulting from oxidization. Another object of the present invention is to provide a system and method that provides a fluid effluent substantially free of salts and particulates while retaining a high destruction efficiency. Still another object of the present invention is to provide a system and method which allows recovery of energy from the high temperature, high pressure fluid effluent. Yet another object of the present invention is to provide a system and method which is easy to implement, simple to use, and cost effective.